Gating apparatus for charged particles



Aug. 14, 1962 J. M. SAARl EI'AL GATING APPARATUS FOR CHARGED PARTICLES Filed June 29, 1959 INVENTORS. JOHN M. SAARI DONALD C. DAMOTH WlLLIAM C.WILEY F'IG-I United States Patent Ofifice 3,849,538 Patented Aug. 14, 1962 3,049,638 GATING APPARATUS FOR CHARGED PARTICLES John M. Saari, Oak Park, Donald C. Damoth, Pontiac,

and William C. Wiley, Northville, Mich, assignors to The Bendix Corporation, a corporation of Delaware Filed June 29, 1959, Ser. No. 823,487 12 Claims. (Cl. 313-103) This invention pertains to a gating apparatus for charged particles and more particularly to an apparatus for receiving and gating an electron stream developed by an electron multiplier.

It is an object of this invention to provide an apparatus for gating an electron stream to one of a plurality of collecting anodes by pulsing the appropriate gate electrode with an electron stream diverting potential wherein the anode is substantially isolated from the eifects of the pulsing voltage.

It is another object of this invention to provide an apparatus for gating an electron stream to one of a plurality of collecting anodes by pulsing an appropriate gate electrode with an electron attracting potential wherein the gate electrode has a transverse metal rod attached at the end thereof to increase gating efiiciency.

It is a further object to provide an apparatus for gating an electron stream to one of a plurality of collecting anodes by pulsing a gate electrode with an electron stream diverting potential wherein an anode plate, which is spaced from the gating electrode and is closely spaced to the collecting anode, has applied thereto a potential for directing the electrode stream to the collecting anode.

It is another object to provide in the previous apparatus a ground plate for covering the spacing between the anode plate and gating electrode of the adjacent collecting anode so as to prevent electrons from passing to the adjacent collecting anode and cooperates with the anode plate to form a field for directing the electron stream to the anode.

Another object is to provide between the gating apparatus and a feeding mechanism, such as an electron multiplier, an area of resistive material which gradually lowers the relatively high potential at the end of the multiplier to lower potential at the mouth of the gating apparatus to maintain beam definition.

A further object is to provide at the end of the multiplier a variable voltage control which controls cycloid size and frequency to control electron multiplication.

These and other objects and advantages will become more apparent when a description of a preferred embodiment is considered in connection with a drawing in which FIGURE 1 shows in partially schematic form a preferred embodiment of this invention and FIGURE 2 is a partial plan view of the embodiment of FIGURE 1 showing the magnetic field source.

In previous electron stream gating systems the gate electrode was used to divert the electron stream to its respective collecting anode and extended to the collecting anode to provide a field which directed the electrons to the surface of the collecting anode. Due to the proximity of the gating electrode to the collecting anode, the pulse applied to the electrode would cause undesirable fluctuations in the anode potential. This invention overcomes this problem by providing a construction wherein the gating electrode is substantially isolated from the collecting anode and yet a proper field is established to direct diverted electrons to the collecting anode. Also, the gating electrode is provided with a transverse metallic rod at the electron receiving end thereof to increase the eifectiveness of the gating action.

In FIGURE 1 is shown a gating assembly which receives electrons from an electron multiplier 22. The multiplier 22 has a cathode 24 from which electrons are emitted due to an energizing signal, a field strip 26, and a dynode strip 28. The field strip 26 and dynode strip 28 are made of an insulative material, such as glass or Bakelite. The field strip 26 has an electrode 30 at one end which may be at a potential such as -1200 volts supplied by a source 31, an electrode 32 at an intermediate portion which is supplied with a variable voltage such as zero to 300 volts from a voltage source 34, and an electrode 36 at the other end which is grounded. Intermediate the electrodes 30, 32 on the inner side which faces the dynode strip is a high resistive, secondary electron emissive coating 38. The dynode strip 28 has an electrode 40 at one end near the cathode 24, which may have an applied voltage of 1500 volts supplied by source 31, an intermediate electrode 42, which may be at a -70 volts supplied by source 31, and an electrode 44 at its other end, which may have applied thereto a volts also supplied by source 31. The coating 46 on the inner side of dynode strip 28 is also a high resistance secondary electron emissive material.

FIGURE 2 shows pole pieces 33 which are on opposite sides of a tube 35 which encloses the multiplier 22 and gating system 20. Connecting pole pieces 33 on either side of tube 35 at spaced longitudinal intervals are magnets 37 which make one pole piece positive and the other negative.

Due to the high resistive material between the electrodes in both field strip 26 and dynode strip 28, a continuous voltage drop is provided. Since the strip ends are at different potentials, an inclined electrical field results and when combined with a transverse magnetic field provided by pole pieces 33. The electrons emitted from cathode 24 are caused to cycloid along the surface of dynode strip 28 with each electron impact emitting a plurality of secondary electrons to provide a secondary emission of increased magnitude. This is more fully explained in the Patent No. 2,841,729 issued July 1, 1958, to W. C. Wiley.

The electrode 32, as mentioned, is supplied with a variable voltage and this is for the purpose of controlling multiplying action. Varying the voltage applied to electrode 32 will vary the potential gradient along field strip 26 to correspondingly vary the cycloid size and action, thereby varying the multiplier gain. Increasing the voltage at electrode 32 will increase the cycloid size and also increase the gain per stage but decrease the number of stages. Therefore, by controlling a relatively low voltage at electrode 32 the number of stages and gain per stage can be controlled. This simplifies amplifier construction since lower voltages are more easily controlled than the higher voltages.

Electrode 42 is more positive than electrode 44 in order to cause the electron cycloid to rise from the surface of the dynode strip so that when it enters gating apparatus 20 spaced charged effects will not drive it into the rail, later described, of the gating apparatus. The inner surface of the field strip 26 between electrodes 32 and 36 is coated with a high resistance material as is the inner surface of the dynode strip between electrodes 42, 44. Due to these resistive surfaces there is a gradual potential change between electrodes 32 and 36 and between electrodes 42 and 44 so that the relatively large potential difference between electrodes 32 and 42 is gradually reduced to the smaller potential difiference between electrodes 36 and 44. Also, the lifting of the electron stream is gradual thereby keeping the stream in more well defined limits to improve accuracy.

The gating mechanism 20 has a longitudinally aligned rail 50 which is made of a conductive material and is connected to and is at the same voltage as electrode 44. The magnetic field extends through the length of rail 50 and the cycloiding action of the electrons continues but the cycloid is raised a predetermined amount so that the electrons do not strike the rail 50 and be absorbed thereby. Spaced laterally from rail 50 and extending upwardly are gating walls 52 which define the gating area and are connected to ground potential. Between the gating walls 52 are a plurality of gating electrodes 54 each of which is spaced laterally or upwardly from rail 50 and each of which has a transverse metal rod 56 welded or otherwise fastened to the lower end thereof. Connected to each of the electrodes 54 is a corresponding pulser 58 which maintains their respective electrodes at zero potential until it is desired to divert the electron cycloid upwardly past the pulsed gating electrode at which time the pulse voltage is lowered to or below the rail voltage. Spaced upwardly of and aligned with each electrode 54 is an anode plate 69 which is maintained at a constant voltage such l() volts by voltage source 61 and adjacent each plate 60 is a collecting anode 62 which is connected to output members, not shown, which may be indicating and/or actuating devices. The anode plates 60 are preferably spaced from anodes 62 a distance less than the cycloid height and provide the proper field to direct an electron cycloid diverted by the corresponding pulsed electrodes 54 to the collecting anode 62. Since the electrodes 54 are spaced from the anodes 62 and have an intermediate field existing therebetween, any pulse applied to the electrodes 54 does not materially affect anode 62. A grounded plate 64 is placed across the adjacent anode 54 and anode plate 60 to prevent electrons from passing therebetween and impinging upon the adjacent collecting anode and provides a ground voltage to maintain a proper electric field across an individual gate.

In describing the operation of this device, a typical cycloidal path 70 emanating from cathode 24 will be considered. The cycloid is formed through the cooperation of the electrical and magnetic fields existing between strips 26 and 28. At each contact point of the cycloid with strip 28, secondary electrons are emitted resulting in a multiplying action. The cycloid moves leftwardly towards the increasing voltage of electrodes 32 and 42. The cycloid size depends on the voltage value of electrode 32, increasing with increased electrode voltage. The cycloid is then gradually lifted from the dynode strip 28 due to the gradual voltage reduction between electrodes 42 and 44 which is made possible by the high resistive coating placed on the inner surface of strips 28 and 32. This gradual lifting of the cycloid from the dynode strip is advantageous since it maintains definition of the electrode stream. Also, the gradual transition provided from the relatively high voltage between electrodes 32 and 42 and the lower voltage between electrodes 36 and 44 maintains definition of the electron stream. By the time the cycloid path reaches the area of rail 50' it has been elevated a predetermined amount and travels longitudinally along the rail. If any one of the gating electrodes 54 is pulsed in an appropriate manner, the cycloid will be diverted towards the collecting anode 62 of the pulsed electrode 54. Assume in this instance that the leftmost gating electrode 54 has been pulsed by its pulser 58, thereby diverting the cycloid in an upward direction towards anode 62. The cycloid continues in an upward direction and due to the field applied to anode plate 60 is directed towards the collecting anode 62. Since anode plate 60 can be maintained at a constant potential the collecting anode 62 is substantially unaifected by the pulsing applied to electrode 54. Electrons are prevented from passing through the spacing between the adjacent electrode 54 and anode plate 60 by grounded plate 64.

Due to the transverse metallic rod 56 fastened to the bottom portion of each electrode 54 any pulses received by electrode 54 will be more elfective in diverting the electron beam. This provides an increased area of field lines so that it is less likely for an electron to continue in its longitudinal path.

The rail 50, gating electrodes 54, anode plates 60 may All he channel shaped to better retain the electron stream passing therealong.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described our invention, we claim:

1. A gating system for an electron stream comprising a longitudinally aligned rail, means to maintain the rail at a predetermined potential, longitudinally spaced gating electrodes being laterally spaced from and inclined to said rail, gate rods being attached to the end of said gate electrodes near said rail, means for pulsing Said gate electrodes to divert the electron stream from the lateral spacing between said electrodes and said rail to the longitudinal spacing between adjacent inclined gate electrodes, a collecting anode being associated with each gate to receive electrons diverted thereby, an anode plate closely spaced to said anode and spaced from said gating electrode, means to maintain said plate at a potential to guide electrons diverted by the corresponding gate electrode to the collecting anode so that said anode is substantially unaffected by the electrode pulses, plate means to cover the spacing between said gating electrode and said anode plate of the adjacent gating channel and being at a potential relative to said anode plate to establish a field therebetween to cause the electron stream to impinge on said anode.

2. A gating system for an electron cycloid comprising a longitudinally aligned rail, means to maintain the rail at a predetermined potential, longitudinally spaced gating electrodes being laterally spaced from and inclined to said rail, gate rods being attached to the end of said gate electrodes near said rail, means for pulsing said gate electrodes to divert the electron cycloid from the lateral spacing between said electrodes and said rail to the longitudinal spacing between adjacent inclined gate electrodes, a collecting anode being associated with each gate to receive electrons diverted thereby, an anode plate spaced nearer to said anode than the height of the cycloid and spaced from said gating electrode, means to maintain said plate at a potential to guide electrons diverted by the corresponding gate electrode to the collecting anode so that said anode is substantially unaffected by the electrode pulses, plate means to cover the spacing between said gating electrode and said anode plate of the adjacent gating channel and being at a potential relative to said anode plate to establish a field therebetween to cause the electron stream to impinge on said anode.

3. A gating apparatus comprising an electron multiplier having a secondary emissive surface means, rail means longitudinally aligned with said emissive surface means, means to maintain said rail means at a predetermined potential, resistive means being interposed between said rail means and said surface means, the voltage difference at the end of said surface means being at one end of said resistive means and the voltage difference at the receiving end of said rail means being at the other end of said resistive means to provide a gradual potential gradient and maintain electron stream definition, longitudinally spaced gating electrode means being laterally spaced from and inclined to said rail means, means for pulsing said gate electrode means to divert the electron stream from the lateral spacing between said electrode means and said rail means to the longitudinal spacing between adjacent inclined gate electrode means, collecting anode means being associated with each gate means to receive electrons diverted thereby.

4. A gating apparatus comprising an electron multiplier having a secondary emissive surface, means for establishing an electrical field having a component normal to said surface, a rail longitudinally aligned with said emissive surface, resistive means being interposed between said rail and said surface and having one end at the potential associated with the surface end field and the other end at the potential associated with the rail end field to provide a gradual potential gradient, longitudinally spaced gating electrodes being laterally spaced from and inclined to said rail, means for pulsing said gate eletcrodes to divert the electron stream from the lateral spacing between said electrodes and said rail to the longitudinal spacing between adjacent inclined gate electrodes, a collecting anode being associated with each gate to receive electrons diverted thereby.

5. The apparatus of claim 4 having a variable voltage member interposed said resistive means and said surface to control the amplifying output of said electron multiplier.

6. A gating apparatus comprising an electron multiplier having a secondary emissive surface, means for establishing an electrical field having a component normal to said surface, a rail longitudinally aligned with said emissive surface, longitudinally spaced gating electrodes being laterally spaced from and inclined to said rail, means for pulsing said gate eletcrodes to divert the electron stream from the lateral spacing between said electrodes and said rail to the longitudinal spacing between adjacent inclined gate electrodes, a collecting anode being associated with each gate to receive electrons diverted thereby, a variable voltage member being connected to the surface end adjacent the amplifying output of said electron multiplier to control electron multiplication.

7. A gating apparatus comprising an electron supplying means having a supplying member, rail means longitudinally aligned with said member, means to maintain said rail means at a predetermined potential, resistive means being interposed between said rail means and said member, the voltage difference at the end of said member being at one end of said resistive means and the voltage difference at the receiving end of said rail means being at the other end of said resistive means to provide a gradual potential gradient and maintain electron stream definition, longitudinally spaced gating electrode means being laterally spaced from and inclined to said rail means, means for pulsing said gate electrode means to divert the electron stream from the lateral spacing between said electrode means and said rail means to the longitudinal spacing between adjacent inclined gate electrode means, collecting anode means being associated with each gate means to receive electrons diverted thereby.

8. A gating apparatus comprising an electron supplying means having a supplying member, means for establishing an electrical field having a component normal to said member, a rail longitudinally aligned with said member, resistive means being interposed between said rail and said member and having one end at the potential associated with the member end field and the other end at the potential associated with the rail end field to provide a gradual potential gradient, longitudinally spaced gating electrodes being laterally spaced from and inclined to said rail, means for pulsing said gate electrodes to divert the electron stream from the lateral spacing between said electrodes and said rail to the longitudinal spacing between adjacent inclined gate electrodes, a collecting anode being associated with each gate to receive electrons diverted thereby.

9. A gating apparatus comprising an electron supplying means having a supplying member, means for establishing an electrical field having a component normal to said member, a rail longitudinally aligned with said member, resistive means being interposed between said rail and said member and having one end at the potential associated with the member end field and the other end at the potential associated with the rail end field to provide a gradual potential gradient, longitudinally spaced gating electrodes being laterally spaced from and inclined to said rail, means for pulsing said gate electrodes to divert the electron stream from the lateral spacing between said electrodes and said rail to the longitudinal spacing between adjacent inclined gate electrodes, means enlarging a portion of said gate electrodes near said rail to increase the gating field upon a gating pulse, a collecting anode being associated with each gate to receive electrons diverted thereby, a variable voltage member being interposed said resistive means and said member to control the amplifying output of said electron multiplier.

10. A gating apparatus comprising an electron supplying means having -a supplying member, means for establishing an electrical field having a component normal to said member, a rail longitudinally aligned with said member, resistive means being interposed between said rail and said member and having one end at the potential associated with the member end field and the other end at the potential associated with the rail end field to provide a gradual potential gradient, longitudinally spaced gating electrodes being laterally spaced from and inclined to said rail, means for pulsing said gate electrodes to divert the electron stream from the lateral spacing between said electrodes and said rail to the longitudinal spacing between adjacent inclined gate electrodes, means enlarging a portion of said gate electrodes near said rail to increase the gating field upon a gating pulse, a collecting anode being associated with each gate to receive electrons diverted thereby, a variable voltage member being interposed said resistive means and said member to control the amplifying output of said electron multiplier, an anode plate closely spaced to said anode and spaced from said gating electrode, means to maintain said plate at a potential to guide electrons diverted by the corresponding gate electrode to the collecting anode so that said anode is substantially unaffected by the electrode pulses, plate means to cover the spacing between said gating electrode and said anode plate of the adjacent gating channel and being at a potential relative to said anode plate to establish a field therebetween to cause the electron stream to impinge on said anode.

11. An electron multiplier having a secondary emissive resistive surface, means for applying a potential difference across said surface so that a gradual potential gradient is established along said surface, and a voltage control near the surface end having the lower absolute value to thereby control the electron multiplication.

12. A gating apparatus comprising an electron multiplier having a secondary emissive surface means, rail means longitudinally aligned with said emissive surface means, means to maintain said rail means at a predetermined potential, resistive means being interposed between said rail means and said surface means, the voltage difference at the end of said surface means being at one end of said resistive means and the voltage difference at the receiving end of said rail means being at the other end of said resistive means to provide a gradual potential gradient and maintain electron stream definition, longitudinally spaced gating electrode means being laterally spaced from said rail means, means for pulsing said gate electrode means to divert the electron stream from the lateral spacing between said electrode means and said rail means to the longitudinal spacing between adjacent gate electrode means, collecting anode means being associated with each gate means to receive electrons diverted thereby.

References Cited in the file of this patent UNITED STATES PATENTS 2,513,260 Alfven June 27, 1950 2,841,729 Wiley July 1, 1958 2,841,741 Wiley July 1, 1958 2,841,743 Haard July 1, 1958 

